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    <script>
        /* ++,-- 
        在算术运算中++在前  先自增，后运算
        ++在后  先运算，后自增
        */
        var a=10;
        a++;   //11
        /* a=a+1 */
        var b=a++ +11;  //22
        /* var b=++a +11;  //23 */
        console.log(b) 

      /*  var a=10;
       a--;
       var b=a-- -2;
       console.log(b) */
    </script>
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